Low profile wheel scale assembly

ABSTRACT

Wheel scale assemblies and load cell structures are provided for weighing loads. The invention provides a low profile portable wheel scale assembly of a predetermined height. The scale assembly has a thin lightweight base structure and a cooperating load platform. At least one load cell structure having strain gauges is in communication with the base structure and the load platform at predetermined locations and configurations. A platform support structure is provided to distribute the platform load. A unitary shear load cell structure contacts the weighing platform and provides a structural weight bearing component. The load cell structure has a unitary symmetrical load cell body. The load cell body has a centrally spanning elongated, deflectable beam structure. Opposing lateral indented beam portions form a central stress isolation web for the structural support and weighing of the load. Strain gauges are mounted in predetermined orientations to the parallel lateral beam walls. And, predetermined load cell configurations and arrangements are provided for low profile weighing scales.

This is a continuation-in-part of application Ser. No. 07/199,478, filedMay 27, 1988, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to wheel scale assemblies and load cellstructures for weighing loads. Particularly, this invention relates toimproved portable electronic wheel scales having predetermined load cellstructures and arrangements to provide lightweight, low profile andaccurate weighing scales.

A co-pending U.S. patent application, now, U.S. Pat. No. 4,813,504entitled, "Load Cell Structure", by Applicant Kroll was granted on Mar.31, 1989. That application further describes and claims improved loadcell structures or assemblies.

Applicant has previously disclosed wheel scale and load cell assembliesin U.S. Pat. No. 4,714,121. The wheel scale assembly of this inventionis of a lower profile, a different structure and also shows the use ofnew and improved load cell structures. Although the present load cellsare also of the shear load cell type, they have different configurationsand function with different cooperating wheel or load platformstructures.

Wheel scales or platform scales are commonly used to measure axle weightloads of vehicles, such as trucks. And, although some platform scaledevices are designed to accommodate the multiple wheels of dual tandemrear axle assemblies of commercial trucks, most wheel scale devices havea single platform to measure the load from single or dual wheels.

In use, a pair of wheel scales are spaced apart and the vehicle isdriven onto the scale platforms one axle at a time. Each axle weightload is recorded and the summation of axle weights yields the grossweight of the vehicle.

Wheel scales utilizing load cells for weighing axle loads of motorvehicles are known in the weighing art. Additionally, wheel scales whichutilize strain gauge sensors fixed to deflectable load cells are known.However, the specific configuration of the load cells utilized in priorart scales, the placement of the load cells in the housing structures ofthese scales, and the cooperation of the active and inactive elements ofthese prior art wheel scale devices often yield complex and bulky wheelscales which are inaccurate and unrepeatable under many conditions ofuse.

For example, prior art wheel scale devices have been proposed andmanufactured to use various types of load cell configurations for thepurpose of yielding a lightweight, low profile and accurate portablewheel scale. Additionally, various wheel scale structures have beenproposed and manufactured wherein these load cell configurations havebeen utilized with varying cooperative elements. However, these priorart wheel scale structures have often been difficult to transport andutilize, have been susceptible to damage, and have required the preciseload placement of loads to achieve reasonable scale accuracy andrepeatability.

Although load cell assemblies are usable in a variety of vehicle scaledevices, there are specific requirements and difficulties associatedwith their use in portable wheel scales used by law enforcementofficers, for example. Such portable wheel scales must be unitary,lightweight and rugged assemblies able to withstand the lateral forcesresulting from the braking and skidding of truck tires.

Additionally, such portable wheel scales are preferably usable on avariety of road surfaces or terrains, should have low or thin profilesto Prevent weighing inaccuracies caused by load shifts and arepreferably accurate and reliable irrespective of precise wheel placementonto the platform structures. The load cell assemblies of this inventionin conjunction and cooperation with the scale housing or base structureand load platform structures provide such a low profile, reliable andaccurate portable wheel scale.

Many types of load cell assemblies have been used or proposed for use inweighing scales as well as in portable wheel scales. And most such useshave required various load cell restraining and retention mechanisms.Depending upon configuration, these load cell fastening or restrainingstructures have often resulted in unreliable and unrepeatable load celloutput. The load cell structures and wheel scale assemblies of thisinvention do not require the use of these load cell restrainingmechanisms.

Despite the need for a truly portable, low profile, sturdy and accuratewheel scale device and load cell structures which overcome the problemsassociated with these prior art weighing scales and load cells, none inso far as is known, has been proposed or developed. Accordingly, it isthe object of this invention to provide a lightweight, fully electronic,self contained, high capacity wheel load scale which has a low profileand which utilizes load cell structures and arrangements that providefor the accurate and repeatable weighing of loads under a broad range ofenvironmental conditions.

SUMMARY OF THE INVENTION

This invention provides a low profile portable wheel scale assembly of apredetermined height. The scale assembly has a thin lightweight base orhousing structure with an interiorly disposed opening having a bottomsurface with means for receiving a load cell structure. At least oneload cell structure having strain gauge means is in communication withthe base structure. The load cell structure is mounted to the receivingmeans of the base structure bottom surface. A platform engagingstructure has means for engaging the load cell structure and means forengaging the wheel platform member. The thin platform member has a flattop surface and a bottom surface with at least one predeterminedindentation for receiving and engaging the platform engaging means.

This invention also provides a unitary shear load cell assemblyconstructed and arranged for direct contact with the weighing platformof a scale assembly and for providing a structural weight bearingcomponent. The load cell assembly has a unitary symmetrical load cellbody structure having a longitudinal axis and having flat peripheralbottom portions. The load cell body has a centrally spanning elongated,deflectable beam structure having a centrally disposed load receivingmeans. The beam structure is defined by spaced apertures through thebody structure. The beam structure has a bottom surface higher than theremaining portions of the body structure. And, the load receiving meansdirectly communicates with the weighing platform of the scale assembly.

A pair of opposing lateral beam portions are indented in the beamstructure and have spacially parallel lateral walls which form a centralstress isolation web and a localized I-beam configuration for thestructural support and weighing of a load. Strain gauge means aremounted in a predetermined orientation to the parallel lateral beamwalls. The strain gauge means is mounted at a perpendicular axis withrespect to each other, each axis being at a predetermined angle withrespect to a plane perpendicular the longitudinal axis of the load cellbody structure.

Provided also by this invention are certain component configurations aswell as materials of construction for these cooperating components. And,provided are methods of utilizing the cooperating elements of the scaleassembly to achieve accurate and repeatable weighing results.

These and other benefits of this invention will become clear from thefollowing description, by reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the low profile electronic wheel scaleassembly of this invention;

FIG. 2 is an exploded view in perspective of the low profile electronicwheel scale assembly showing the cooperating elements thereof;

FIG. 3 is a top view of the base or housing portion of the low profileelectronic wheel scale assembly of FIG. 2;

FIG. 4 is a cross-sectional view of the base portion shown in FIG. 3,taken along line A--A;

FIG. 5 is a cross-sectional view of the base portion shown in FIG. 3,taken along line B--B;

FIG. 6 is a bottom view of the wheel or load platform of the low profileelectronic wheel scale assembly of FIG. 2;

FIG. 7 is a cross-sectional view of the wheel platform shown in FIG. 6,taken along line C--C;

FIG. 8 is a top view of the load cell assembly of the low profileelectronic wheel scale assembly of this invention;

FIG. 9 is a cross-sectional view of the load cell assembly shown in FIG.8, taken along line D--D;

FIG. 10 is a side view of the load cell assembly shown in FIG. 8 whichfurther shows the apertures therein;

FIG. 11 is a cross-sectional view of the load cell assembly shown inFIG. 8, taken along line E--E;

FIG. 12 is another cross-sectional view of the load cell assembly shownin FIG. 8, taken along line E--E, showing a specific strain gaugeconfiguration;

FIG. 13 is another cross-sectional view of the load cell assembly shownin FIG. 8, taken along line E--E, showing another strain gaugeconfiguration;

FIG. 14 is a top view of another embodiment of the platform structure ofthe low profile electronic wheel scale assembly of this invention;

FIG. 15 is a cross-sectional view of the platform structure shown inFIG. 14;

FIG. 16 is a bottom view of another embodiment of the wheel or loadplatform of the low profile electronic wheel scale and showing its castaluminum lower portion assembly;

FIG. 17 is a cross-sectional view of the wheel platform shown in FIG. 6,taken along line F--F;

FIG. 18 is a cross-sectional view of the wheel platform shown in FIG.16, taken along line G--G;

FIG. 19 is a top view of the steel top portion utilized with the wheelplatform embodiment shown in FIG. 16;

FIG. 20 is a perspective view of another embodiment of the load platformstructure of the wheel scale assembly of this invention;

FIG. 21 is a lateral view of the wheel platform structure of FIG. 20;

FIG. 22 is a perspective view of another embodiment of the unitary loadplatform structure and having cutaway portions to show its construction;

FIG. 23 is a sectional view of FIG. 22 taken along lines 23--23; and

FIG. 24 is a sectional view of FIG. 22 taken along lines 24--24.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the low profile electronic wheel scale assembly 10of the present invention is shown having a base or housing structure 11,a wheel or load platform 12, a control/readout system 56, and a handleportion 57. The wheel platform 12 is disposed on the top of the basestructure 11 to provide a low profile structure for supporting thewheel(s) of a vehicle or other load for weighing purposes. Entrance endsor sides 85 and 86 of the low profile wheel scale assembly 10 areutilized to provide a ramp access to the wheel platform 12 for vehiclewheels.

The wheel scale assembly 10 according to the invention provides alightweight, electronic, self contained, high capacity wheel load scale.For example, one such scale has a capacity to weigh loads up to 60,000lbs. with an accuracy of ±1%; the preferred weighing range being in therange of from 0 to 20,000 lbs. However, the teachings of this inventionare also applicable to scales having other weight capacities. The wheelscale assembly 10 will operate accurately on a variety of surfacesincluding asphalt, concrete, crushed stones, gravel, hard packed soil,and soft ground without the use of risers or an additional base plate.Further, the water resistant, moisture resistant, and dirt resistantwheel scale assembly 10 is usable under all weather conditions and in atemperature range of, for example, from 14 to 122 degrees Fahrenheit.

The base structure or housing 11, and wheel or load platform 12 of thewheel scale assembly 10 are preferably constructed of high strength castaluminum or a similar sturdy and durable material. The base structure 11Preferably has a grooved, nonskid surface on its bottom to preventslipping and skidding of the wheel scale assembly 10 during use. Thewheel scale assembly 10 has a very low profile or height. The wheelscale assembly 10 preferably has a height of approximately 1.5 inches orless which has been found suitable for use as a portable scale by lawenforcement officers, for example, for use in vehicle load restrictionenforcement. This low profile provides easy wheel access to the wheelplatform 12 without the need for large ramp structures and also providesincreased weighing accuracy and durability.

FIG. 2 illustrates the various external and internal components of thewheel scale assembly 10 of this invention. The base structure 11 andwheel platform 12, described in further detail below, are shown as beinggenerally rectangular and substantially coextensive in dimension witheach other, for example, approximately 15.0×22.5 inches. The basestructure 11 further has an open interior cavity with a substantiallyflat bottom surface 39. A plurality of low profile load sensing devices14, preferably four as shown in FIG. 2, are mounted on the bottomsurface 39 of the base structure 11 at predetermined locations and in apredetermined orientation with respect to the lateral sides or entrancesides 85 and 86. The load sensing elements 14 are preferably load cellstructures detecting shear strain. The load cells are described indetail below and further in Applicant's co-pending U.S. patentapplication for "Load Cell Structure". Platform support structures orload support plates 15 are connected to the load cells 14 and to thewheel or load platform 12 to provide increased structural strength forhigher load bearing scale capacity while maintaining a low profile scalestructure. Thus, the platform support structures 15 permit the platform12 to have a lower profile.

The control/readout system 56 comprises a keypad housing 43 which ispreferably integrally formed with the base structure 11 and composed ofcast aluminum materials. The cast aluminum structure provides fullEMI/RFI immunity for its internal circuitry. The keypad housing 43 hasan open cavity at its top and houses the electronic components 21 andpower source 22 of the system 56. The electronic components 21 of thesystem 56 are preferably disposed on a printed circuit board 47 forspacial economy, durability, and ease of manufacture and repair. Thecircuit board 47 is mounted within the keypad housing 43 on shockabsorbing mounting elements 52 via screws 30. The circuit board assembly47 is connected to the load cell structures 14 via a series ofinterconnect wiring (not shown).

Fixed to the control/readout system 56 is the replaceable handlestructure 57 having a handle member 13 connected to opposing handlebraces 44 via screws 26. Alternatively, the handle member 13 may beintegrally formed with the cast aluminum handle braces 44. The handlestructure 57 is angled upwards to allow full hand access for lifting ofthe wheel scale assembly 10 without contacting the ground or other scale10 parts.

The circuit board assembly 47 includes an amplifier, a filter, an analogto digital converter, a microprocessor, a memory and a liquid crystaldiode (LCD) or similar display 46. The microprocessor provides thefollowing control features: automatic test; low power indication,malfunction alerting; automatic power down after a fixed period of time,for example, 10 minutes; auto-zero tracking; digital weight averaging;and manual calibration adjustment. The LCD display 46 is preferablyconnected to the circuit board assembly 47 via an elastomeric electricalconnector 45 such as a STAX connector manufactured by PCK Elastomerics.The printed circuit board 47 is coated with a sealant which protects itfrom moisture and fungus, but which also allows repairs to be made tothe circuit board 47 components. The circuit configuration 47 is alsoinsulated from the remaining elements of the wheel scale assembly 10 toprevent accidental shock while in use.

The electronic components 21 are powered by a battery pack 22, whichconsists, for example, of six "AA" 1.2 volt Ni--Cd batteries which arerechargeable, without removal, at the external connector 23. Theexternal connector 23 is connected to the keypad housing 43 at anaperture 59 and has a connector cap 32. The batteries are preferablywelded together in series and secured by a plastic heat shrink tubing.Such a battery pack 22 configuration provides easy removal andreplacement of batteries without the use of tools, and also preventsbattery corrosion from contaminating the remaining electricalcomponents. A connector cap 19 and sealing O-ring 24 prevent entry ofdirt and moisture, and maintains the battery pack 22 in a constantposition for weighing operation which also avoids power loss. Thisconfiguration further provides shielding from electrical interferenceduring charging, such as starting of the vehicle, radio transmission, orother electrical accessories. The battery pack 22 is insertable into thehousing extension 43 at a threaded battery port 34 located at the sideof the housing extension 43.

The external connector 23 also is designed for cable connection tocommunicate with additional scale assemblies 10, as will be discussedwith respect to the operation of the scale assembly 10.

As further shown in FIG. 2, the control/readout system 56 has aprotective face plate or bezel 18, a key pad 20 which has a number ofswitches, a key pad support 17, and a bezel gasket 16 which are sealablyconnected to the top edge of the keypad housing 43 via screws 29 inthreaded apertures 54. These layered elements have apertures throughwhich the display 46 is extended. The switches are preferably of apressure sensitive waterproof membrane type. An "on" switch, whenactivated, causes the scale 10 to test all of the segments on thedisplay 46 and then zero itself. There is also provided, a separate"off" switch for unambiguous operation by the operator. A "print"switch, when activated, transmits data via a connecting cable to anotherscale, printer or display (not shown). A "weight unit selector" switchprovides optional reading in either pounds or kilograms. A "local/total"switch, permits a user to display either the weight on the specificscale 10 used (local) or to sum the total weight from a plurality ofscales (total). A "test" switch tests the display 46 function byactivating all of its segments. A "lamp" switch activates a lightlocated behind the display 46 for night use. A "hold/release" switchpermits the scale 10 to be in a "hold mode" where the scale 10 locksonto the first steady weight of 50 lbs. or greater for use in "inmotion" weighing. When released, the scale display 46 will indicateactual weights.

Referring to FIGS. 3-5, the base structure 11 has vertical side walls 40surrounding an open central cavity having a flat bottom 39. The sidewalls 40 have an angled portion 49 and a flat top 50. The angled portion49 aids ongress and egress of vehicle wheels onto the scale assembly 10.The base structure 11 further has a plurality of generally rectangularload cell recesses 38 and integrally connected interconnect wiringrecesses 41. The recesses 38 and 41 are approximately 1/8 inch deepindentations in the bottom surface 39 of the base structure 11 and areprovided via a machining process. The recesses 38 and 41 are desireablewhere the base structure 11 is composed of cast aluminum (which yields arelatively rough finished surface) to provide a uniformly flat surfacefor load cell 14 function. The load cell recesses 38 have a horizontaldimension generally coextensive with that of the load cell structures14. The load cell recesses 38 further have rounded and slightly enlargedcorners to ensure the fit of the load cells 14 thereon. Apertures 42 areprovided to receive flathead screws 27 for attachment of the load cells14 to the base structure 11. The interconnect wiring recesses 41 extendfrom each load cell recess 38 to meet at the end of the cavity 39proximate the keypad housing 43, thereby forming a generally branchedconfiguration. A plurality of interconnect wiring apertures 53 aredisposed in the base structure 11 wall between the central cavity 39 andthe keypad housing 43 for extension of the interconnect wiringtherethrough. Additionally, a sealant composition, such as apolyurethane, is preferably packed in the fitted apertures 53 to providean environmental barrier.

Referring to FIGS. 6 and 7, the wheel platform 12 has a flat top surfaceand a molded bottom surface. The horizontal dimensions of the wheelplatform 12 are generally coextensive with that of the base structure11. Specifically, the wheel platform 12 top surface has a peripheraledge 33 with dimensions equal to the outside dimension of the basestructure 11 flat top 50. The wheel platform 12 bottom surface area isindented or recessed slightly inward from the top surface edge 33 andforms an edge 51. The dimensions of the bottom edge 51 are equal to theinside dimension of the base structure 11 vertical wall 40 so that asthe wheel platform 12 is placed in its operative position on the top ofthe base structure 11, its top edge 33 is aligned with the top edge 50of the base structure 11. And, in this position, the bottom edge 51registers with and is received by the interior cavity 39 of the basestructure 11, within the inside dimension of the vertical wall 40. Thisbase structure 11 and cooperating wheel platform 12 configuration yieldsa composite wheel scale structure 10 which allows vertical displacementof the wheel platform 12 for accurate and stable weighing, but whichalso controls horizontal displacement to prevent detrimental sideloading effects. The configuration further provides a wheel scale 10periphery which is accessible to vehicle wheels.

The wheel platform 12 bottom surface also has a plurality ofindentations or pockets 61 which define perpendicular structural ribmembers 60. The pockets 61 reduce the weight of the cast aluminum wheelplatform 12. Machined load cell recesses 63 are disposed in the bottomsurface of the wheel platform 12. The load cell recesses 63 are alignedwith the load cell recesses 38 of the base structure 11 when the wheelplatform 12 and base structure 11 are in operative registration; therecesses 63 and 38 having coextensive horizontal dimensions forenclosure of the load cell structures 14. Apertures 35 are provided toreceive flathead screws 28 for attachment of the platform supports 15,via threaded apertures 36, to the wheel platform 12. Wiring extensions64 are integrally formed with the load cell extensions 63 foraccommodation of the interconnect wiring.

An additional embodiment of the base structure 11 and wheel platform 12may be utilized with the wheel scale assembly 10, consistent with theteachings of this invention. Referring to FIGS. 16-19, an alternateembodiment of the wheel scale platform 12 is shown to comprise a castaluminum bottom portion 94, approximately 0.75 inches in thickness, anda steel top portion 95, approximately 0.1196 inches in thickness. Thebottom portion 94 has load cell apertures 96 which extend fully throughthe structure. Screw apertures 97 are provided to directly connect thewheel platform top portion 95 via screw means. The wheel platform topportion 95 has screw apertures 98 which align with the screw apertures97 of the bottom portion 94 for direct connection via the screw means.Also, screw apertures 99 are aligned with load cell apertures 96 fordirect connection to platform supports 15 via screw means. The topportion 95 and bottom portion 94 have outer dimensions equivalent tothose of wheel platform periphery 33 and periphery 51 respectively. Thiscomposite wheel platform structure, although heavier, yields a slightlythinner or lower profile scale assembly having substantially the sameload bearing strength.

The composite wheel platform may be utilized with a base structureembodiment composed of approximately 0.1196 inch thick steel with auniformly flat bottom surface similar in configuration to base structure11 to further decrease the overall height of the scale. Because of theincreased weight of the relatively stronger steel material, theresultant scale assembly has a weight increase in comparison to atotally cast aluminum structure. However, the steel/aluminum sandwichedstructure provides a thinner wheel scale 10 having a thickness ofapproximately 1.18 inches (30 mm.).

Referring again to FIG. 2, the platform support or load support plates15 are disposed between the load cells 14 and the wheel platform 12. Therigid platform supports 15 have horizontal dimensions generallyequivalent to those of the load cells 14 and are composed of hardened1095 spring steel or the like. Additionally, a closed cell polyurethaneor a like construction gasket 31 is disposed between the platformsupports 15 and the load cells 14 to aid in the manufacturing processand containment of sealant compositions to the load cells 14, as will befurther described below. The platform supports 15 are connected to theload cells 14 via screws 25 through central platform support apertures74 inserted into threaded load cell apertures 55. The platform supports15 provide rigidity and strength to the cast aluminum wheel platform 12at its recessed areas which transfer load to the load cells 14 formeasurement purposes.

FIGS. 14 and 15 show another embodiment 70 of the platform supportstructure. The platform support 70 has a raised, convex center portion71 generally coextensive with the load cell 14 dimensions, and aperipheral horizontal, flanged rim portion 72. The convex center portion71 has a central aperture 74 for connection to the load cell 14, whilethe rim portion 72 has a plurality of rim apertures 73. When in itsoperative position, the convex center portion 71 is in registration withthe load cell recess 63 of the wheel platform 12 and with the load cell14, while the rim portion 72 registers with the thicker portions of thewheel platform 12 immediately surrounding the load cell recess 63. Inthe use of this embodiment of the platform support 70, the screwapertures 35 of the wheel platform 12 are disposed in the thicker bodystructure of the wheel platform 12 immediately surrounding the load cellrecess 63, so that they correspond with the rim apertures 73 of theplatform support 70.

This platform support 70 structure provides increased strength to thewheel platform 12 and enhances load-bearing capacity through lateralload transfer. A load imparted to the relatively thinner load cellrecess 63 areas of the cast aluminum wheel platform 12 is transferred tothe steel central portion 71 of the platform support 70 (via directcontact therewith) and distributed laterally to the rim portion 72. Therim portion 72 is bolted, via screws 28 and the apertures 35 and 72, tothe thicker portion of wheel platform 12, and hence yields increasedload bearing capacity.

Referring to FIGS. 8-13, the symmetrical, self-supporting,self-contained and sealed load cells 14 are comprised of a flat,generally rectangular body structure 65 approximately 0.75 inches inheight, having elongated peripheral body portions 75 for support and anelevated, double-ended, shear beam structure 92. The beam structure 92is integrally formed with and longitudinally extends from one end of thebody structure 65 to its other end along axis 78. A pair of open andpreferably urethane filled cavities 66 in the body structure 65 aredisposed on each side of the beam structure 92. The elevated beamstructure 92 forms a beam deflection space 91 between its bottom surface77 and the flat bottom surface 76 of the peripheral body portions 75.

The beam structure 92 is shown to have a generally square load bearingsurface 67 which is centrally disposed on the beam structure 92 andelevated from the peripheral body portions 75. Other load bearingsurface configurations are within the purview of this invention. Stressisolation areas 68 are located on both sides of the load bearing surface67 in the beam structure 92. Each stress isolation area 68 is a uniformnarrowed region of the beam structure 92 which has side walls 82 on bothsides thereof to provide localized stress measurement areas in the beamstructure 92. Apertures or recesses may be disposed in each side of eachstress isolation area 68 for mounting the opposing strain gauges 81 and83 to further provide increased stress isolation and to lessen torsionalor twisting effects of the load cell body 65.

The strain gauges 81 and 83 are oriented on the opposing sides 82 of thestress isolation areas 68, as shown in FIGS. 12 and 13 and furtherdiscussed below, to compensate for tension and compression forces in thebeam structure 92. Strain gauges 81 and 83 are typically instrumentaldevices used to measure dimensional changes within or on the surface ofa specimen, such as a load cell 14. The electrical-resistance straingauge is a commonly used device for strain measurement. Its operation isbased on the principle that the electrical resistance of a conductorchanges when subjected to a mechanical deformation, i.e., due to weighton a load cell. The electrical conductor is bonded to the load cell 14with an insulating cement, such as an epoxy with an acrylic outercoating, under no-load conditions. Thereafter, urethane is provided tothe apertures 66, thus yielding a fully sealed load cell structure 14. Asubsequent load, therefore, produces a deformation in both the load cell14 and in the strain gauge 81 and 83 resistance elements.

Although a number of resistance strain gauge types are known, i.e., wiregauge, foil gauge and semi-conductor gauge, the bonded strain gauge isshown used in the load cells 14 of this invention. The bonded straingauge, 81 or 83, as is known in the art, consists of lead wires 90 andactive resistance wires which are mounted on a carrier sheet. To obtainmaximum performance, the active resistance wires are mounted or cementedas near as possible to the gauging surface 82 of the load cell 14. Thus,when the active wire is stretched elastically, its strength and diameterare altered which results in a change in its electrical resistance. Themeasurement of this resistance change is the principle of operation ofthe gauge 81 or 83 in accordance with Poisson's ratio, crystaldislocation and elongation.

The cooperating flat peripheral body portions 75, elevated double endedbeam structure 92, and beam deflection space 91 of the load cellstructure 14 permit small, free vertical movement and shear deformationof the stress isolation areas 68. Thus, as a load or force is placed onthe wheel platform 12, it is transferred directly to the load cell 14via the platform support 15 or 70. As the force is exerted on the loadcell 14, the stress isolation areas 68 are disfigured. Thisdisfiguration causes the strain gauges 81 and 83 to be proportionallychanged in configuration.

Importantly, the orientation and configuration of the load cells 14 withrespect to the wheel platform 12 permits the proper deflection of theload cell beam structure 92 without potentially damaging side loadeffects and torquing. FIG. 2 shows the load cell 14 beam structures 92being properly oriented perpendicularly with respect to the entrancesides 85 and 86 of the wheel scale 10. In this orientation, the beamstructure 92 axis 78 is aligned in the direction of wheel or loadmovement. Thus, the load cell 14 is in an orientation designed tomaximize strength and to withstand the effects of rapid load movementdue to vehicle double clutching and braking.

The proper orientation or gauging of the strain gauges 81 and 83 on eachmounted and aligned load cell 14 permits accurate weighing irrespectiveof the exact location of the load relative to the top of the wheelplatform 12, for example due to uneven load placement or wheel scale 10tilting. As shown in FIG. 12, strain gauges 81 and 83 are mounted on theopposite sides 82 of the stress isolation areas 68. Strain gauges 81 aremounted perpendicular to one another and at an angle of approximately 45degrees with respect to the plane of the load cell 14 so that they aredirected towards the center 67 of the beam 92. Strain gauges 83 aresimilarly mounted on the opposite walls, however, they are directed awayfrom the center 67 and are therefore spacially perpendicular to straingauges 81. Utilizing this strain gauge 81 and 83 configuration, therespective load cells 14 are preferably gauged so that the correspondingbeam walls 82 of adjacent load cells 14 alternate between theconfiguration of strain gauges 81 and the configuration of strain gauges83. In other words, where the beam walls 82 of a load cell 14 havegauges 81 directed towards beam center 67, the corresponding beam walls82 of the adjacent parallel load cell 14 will have gauges 83 directedaway from the beam center 67. It has been found that utilizing thisstrain gauge 81 and 83 configuration in respective cooperating loadcells 14, the compressive and tensive forces on the several load cellsare balanced to yield accurate and reproducable electrical responsesunder uneven load conditions; the uneven load effects being cancelled bythis strain gauge configuration in a cooperating load cell arrangement.

FIG. 13 shows an alternate strain gauge configuration wherein straingauges 81 are located on the same adjacent walls 82 of the beamstructure 92 and in a spacially parallel configuration at 45 degreeangles with respect to the horizontal plane of the load cell 14. Straingauges 83 are similarly positioned on the opposite side walls of beamstructure 92, parallel to one another, but spacially perpendicular tostrain gauges 81. This strain gauge configuration has also been found toyield accurate and reproducible electrical responses. It has been foundthat utilizing this strain gauge configuration, adjacent and cooperatingload cells 14 need not be alternately gauged on their corresponding beamwalls 82 as discussed with respect to FIG. 12. Thus, this strain gaugearrangement in cooperating load cell configurations yields a structurethat provides the benefits of the alternately gauged load cellconfiguration discussed above.

Referring to FIG. 8, the center axis 78 is shown longitudinallyextending through the load cell 14. The strain gauges 81 and 83 aremounted in a spacially vertical configuration with respect to centralvertical plane "Z". And, referring to FIG. 3, longitudinal axis "X" isshown extending through the center of housing 11 and transverse axis "Y"along the width and through load cell recesses 42. The individual loadcell configuration shown in FIG. 12, having the opposing perpendicularpairs of strain gauges 81 and 83, therefore, are preferably mounted inthe same alignment along axis "Y" but in an opposite orientation when afour pair load cell arrangement is used. Thus, the second pair ofaligned load cells 14 are oppositely mounted in recesses 38 spaciallyfrom the "Y" axis and parallel to the first pair of aligned load cells.The preferred load cell configuration shown is FIG. 13, having theopposingly parallel pairs of strain gauges 81 and 83, can be mounted inany manner along axis "X" or "Y" to achieve a multiple load cellarrangement which effectively cancels side load effects. The latterstrain gauge configuration (FIG. 13) being better suited for multipleload cell use from a manufacturing standpoint.

All four strain gauges 81 and 83 are electrically connected to acircular connecting plate assembly (not shown) proximate the threadedwiring aperture 84 in the peripheral body portion 75. As known, thegauges are connected essentially to the four corners of a wheatstonebridge on this plate or donut and the load cell is there calibrated. Theconnecting plate assembly is connected to the interconnect wiring via acompression fitting 37 disposed in the aperture 84. Preferably,waterproof sealant is disposed in the connector 37 as an environmentalbarrier.

The load cells 14 are preferably composed of 4340 chrome-molybdenumsteel or the like for high strength and reliable deflection. Threadedapertures 69 are disposed in the base structure 65 of the load cells 14.These apertures receive screws 27 through apertures 42 for mounting ofthe load cells 14 to the base structure 11 of the wheel scale assembly10. Threaded aperture 55 is centrally disposed in the load contactingmember 67. This aperture receives screw 25 for mounting of the platformsupport, which is fastened to the wheel platform 12.

FIG. 20 shows a perspective view of another embodiment of the loadplatform structure 100 of the wheel scale assembly of this invention.The load platform structure 100 is shown to be comprised of a top plate101, a wheel platform body 102 and four support plates 104 which arefastened into a unitary structure by screws 111 and 115. The loadplatform body 102 is shown to have four load or wheel cell apertures 103with peripheral support plate recesses 105 whereon plates 104 aredisposed. The plates 104 are attached to the top plate 101 and are alsoattached to the recess areas 105 as well as to the load cell structureapertures 55 as shown in FIG. 8.

A plurality of drilled and countersunk apertures 106 are shown disposedabout the periphery as well as through several interior portions of thetop plate 101 for securing the plate 101 to the load platform body 102.Threaded apertures 107 are provided in the platform body 102 to receivethe screws 115. As further shown, drilled and countersunk apertures 108are disposed in top plate 101 and which are aligned with apertures 110in the support plates 104 and the threaded apertures 109 which aredisposed in the peripheral recess areas 105. Screws 111 are utilized tosecure the support plates 104 between the top plate 101 and the platformbody 102. To complete the assembly of this load platform structure 100,drilled and countersunk apertures 112 are disposed in top plate 101which are aligned with centrally disposed apertures 113 in support plate104 and which receive screws 114 so that this assembly is fastened tothe centrally disposed threaded aperture 55 of each load cell structure.

Thus, the load platform structure 100 provides a three part, unitarystructure which utilized flat, planar support plates 104 disposedbetween the top plate 101 and the load platform body 102. Thisconfiguration provides the necessary strength required to deal withwheel loads encountered during the weighting of trucks, for example,while minimizing the overall weight and height of the scale assembly.The top load plate 101 is preferably constructed of stainless steel, theload cell support plates 104 are preferably of a high constructed ofaluminum.

The bottom plate 102 preferably has a bottom configuration as shown inFIG. 6, having ribs 60 and recesses or pockets 61. It has been foundthat utilizing that plate structure 102 in an upside down manner so thatthe elements 60 and 61 are adjacent the top plate 101 yields a strongand preferred load platform structure 100.

FIG. 22 shows a perspective view of another embodiment of the loadplatform structure 117 used in the wheel scale assembly of thisinvention. The platform structure 117 is a unitary structure which iscomprised of top plate 118, bottom cup plate 119, load cell covers 120,rib structures 123 and rib structure portions 124 which are all unitedby welds 127.

The plates 118 and 119, the covers 120 and ribs 123 and 124 arepreferably constructed of twelve gauge 4130 steel which provides a highstrength steel composition that can be welded to yield a unitary andthin load platform structure which is capable of supporting moving heavyloads. As further shown in the sectional views of FIGS. 23 and 24, theload cell covers 120 are fixed to the bottom surface of the top plate118 so that their respective apertures 122 and 121 are aligned. Thelatter apertures receive the screws that mount the platform structure117 to each load cell. The bottom cup plate 119 is further shown to befixed to the top plate 118 and the rib structures 123 and 124 are fixedtherebetween to provide strength to the unitary structure 117. Slottedapertures 125 and 126 are provided respectively in the bottom plate 119and covers 120 so that the vertical movement of the platform structure117 does not interfere with the wiring extending from the load cells.

As shown in FIGS. 23 and 24, the welds 127 unite the parallel ribsections 123 and 124, the rectilinear cover 118 and reinforcingstructures 120 and the bottom plate 119. The bottom plate 119 is shownto have an angular end portion and a plurality of apertures 128 whichare utilized for welds 127 to unite the rib structures 123 and 124 toplate 119. Other means of uniting these cooperating elements to form theunitary load platform structure 117 are within the purview of thisinvention. The utilization of welds 127 is well suited for high strengthsteel and welds 127, for example, along the entire top exteriorperiphery joining the top plate 118 and the cupped bottom plate 120yields a sealed unitary configuration that is light in weight, has highstrength and provides cavities 129 which directly engage a load cell.

The load cell assemblies shown and described are further disclosed inKroll, LOAD CELL ASSEMBLY, U.S. Pat. No. 4,813,504, issued Mar. 21,1989, are adapted for use in the load scale assemblies disclosed herein.However, other load cell structures can also be utilized as well asdiffering numbers of load cells in accordance with the teachings of thisinvention.

Alternative load cell embodiments known in the art may also be usablewith the wheel scale assembly 10 of this invention, for example, loadcells preferably sensing shear strain, including those effectivelygauged as a beam. The important considerations being the low profile inaccordance with the dimensions of the base structure 11 and that theyare capable of reliable and reproducible results particularly when usedin a load cell arrangement.

Other load cell structures may be devised utilizing the teachings ofthis invention, for example, load cell structures having non-rectilinearbodies or having more than one beam radiating from its load cell center.For example, a four-sided and double beamed structure would double theeffective capacity of the wheel scale assembly 10.

Additionally the load cell structures of this invention are usable in avariety of weighing applications in addition to their use in portablewheel scales. The load cells 14 are self contained, self supporting andhave a low profile; they can be utilized as a single structure and incooperative load cell arrangements.

As many changes are possible to the embodiments of this invention,utilizing the teachings thereof, the descriptions above, and theaccompanying drawings should be interpreted in the illustrative, and notin the limited sense.

That which is claimed is:
 1. A low profile, high capacity, portable andhand movable wheel load scale assembly of a predetermined heightcomprising:(a) a thin lightweight base structure having a length, awidth and a central axis and further having an interiorly disposedopening having a bottom surface with means for placement and securing ofload cell structures, (b) at least one pair of unitary load cellstructures, each said load cell structure having strain gauge meansmounted in a predetermined configuration, each said load cell structurefurther being mounted in a predetermined arrangement transverse saidcentral axis and to said bottom surface placement means, and (c) ametallic planar load platform member having a top surface and a bottomsurface with recesses at predetermined locations, each said bottomrecess for receiving a load cell structure, each said bottom recessfurther having a rigid platform support structure having means forsecuring said platform support structure to said load platform memberand to each said load cell structure.
 2. The low profile portable wheelscale assembly of claim 1, wherein each said platform support structureis comprised of an inverted cupped metallic member having a flangedperiphery for mounting in said wheel load platform member and having acentral portion for nesting in said bottom recess of said platformmember and further having means for connection to said load cellstructure.
 3. The low profile portable wheel scale assembly of claim 1,wherein said load cell placement means of said base structure and saidpredetermined recesses of said platform member have spacially parallelhorizontal dimensions coextensive with each other and with each saidload cell structure.
 4. The low profile portable wheel scale assembly ofclaim 1, wherein each said platform support structure is comprised of aflat metallic plate member.
 5. The low profile wheel scale assembly ofclaim 1, wherein said predetermined height of said wheel scale assemblyis equal to or less than 1.5 inches.
 6. The low profile portable wheelscale assembly of claim 1, wherein said base structure comprises a lowprofile vertical wall about the periphery of said bottom surface, saidwall having an exterior downwardly angled upper edge, and wherein saidplatform member bottom surface has a horizontal dimension slightly lessthan the inside dimensions of said base structure wall periphery forvertical movement thereinto, said platform member top surface having ahorizontal dimension constructed and arranged so that it cooperates withsaid base wall angled upper edge to provide a sloping entry peripheralsurface for said scale assembly.
 7. The low profile portable wheel scaleassembly of claim 1, wherein said securing means of said supportstructure comprises at least one first aperture having first fasteningmeans associated therewith and being connectable to each said load cellstructure and at least one second aperture having second fastening meansassociated therewith for securement in said bottom recess.
 8. The lowprofile portable wheel scale assembly of claim 1, wherein said loadplatform member has a bottom body portion that is comprised of a castaluminum structure having a horizontal dimension to permit verticalmovement into said base structure interior opening, said recessescomprising apertures in said bottom body portion, said load platformmember further having a rigid metallic, top plate portion mountedthereon.
 9. The low profile portable wheel wheel scale assembly of claim1, wherein said load platform member further comprises a metallic topplate, a metallic cupped bottom plate having peripheral side walls and alongitudinal axis and further having longitudinally extending ribsdisposed along its length and fixed between said top and bottomsurfaces, said load platform member recesses comprising indentations insaid bottom plate, said platform support structures being unitary withsaid cupped bottom plate and having means to fasten said load platformmember to each said load cell structure, said cupped bottom platefurther having dimensions to provide vertical movement into said basestructure interior opening.
 10. The low profile portable wheel scaleassembly of claim 1, wherein said load platform member further comprisesa metallic rigid body member, said load platform member recessescomprising apertures therein, and being in alignment with each said loadcell structure and having peripheral recess areas about each saidaperture, said load platform member further comprising a coextensive topplate structure, said platform support structures being mounted in saidperipheral recess areas for attachment to said load cell structure.